1. Field of the Invention
The present invention relates to a particle board for use as a structural material or a furniture component and a method of making the same.
2. Description of the Related Arts
Particle boards are panel-like products made by bonding wooden materials with an adhesive. Most of such particle boards have a three-layer construction consisting mainly of a core layer and two face layers formed on both, front and back, sides of the core layer. The core layer comprises relatively large sized wooden materials hence creating visually recognizable voids. To the contrary, the face layers comprise relatively small sized wooden materials hence being close structure.
Such particle boards are made by supplying wooden materials with a spray of an urethane adhesive, forming, and pressurizing them with heating. The urethane adhesive is hardened when its isocyanate reacts on a hydroxy functional group in the wooden materials. The amount of the adhesive may be approximately from 5 to 10 percent and at the maximum approximately 15 percent on the basis of the whole weight of the wooden materials.
However, while the particle board is functioning sufficiently as a bearing board member, which is unfavorable in the resistance to water because its components are mainly wooden materials. This is, the wooden materials have a hydrophilic property because of its hydroxy functional group.
As the particle board is poor in the function of resistance to water, its water-content gradient may cause deflections and dimensional changes of its structure or its water remaining may result in the development of mold and the decomposition of wooden constituents.
We, the applicants, invented a method for improving the resistance to water of a particle board without impairing its bearing property where a particle board is provided with two plastic sheets bonded to the front and back sides thereof, hence forming an integral structure. However, the prevention of water penetration through the butt ends into the particle board has not yet been achieved. It is hence necessary to improve the resistance to water while further contemplating the internal structure of the particle board.
It is an object of the present invention, in view of the foregoing drawback, to provide a particle board which is improved at its entirety in the resistance to water without impairing its performance as a bearing board member and to provide a method of making the same.
A particle board having wooden materials coated with an adhesive of a thermosetting resin and pressurized with being heated, the particle board comprising: a core layer and face layers provided on both, front and back, sides of the core layer, wherein the wooden materials of the face layer are smaller in the average particle diameter than the wooden material of the core layer; and voids between the adjacent wooden materials in the face layer and the core layer are filled with resin particles of a thermoplastic resin by being pressurized with being heated.
In the particle board of the present invention, the voids between the wooden materials are filled with the resin particles of the thermoplastic and the wooden materials are then pressurized while being heated. This allows the particle board to be filled at not only the surfaces but also the interior with the thermoplastic resin having hydrophobic character. Accordingly, the resistance to water of the particle board will be improved throughout its whole structure.
While the voids between the wooden materials are filled with the resin particles, the wooden materials are securely bonded one another by the thermosetting resin. This provides a substantial resistance to load exerted on the front, back, left, and right sides. Accordingly, the particle board of the present invention will function sufficiently as a bearing board member.
Preferably, the average particle diameter of the resin particles in the face layers is smaller than that of the resin particles in the core layer.
This permits the resin particles and wooden materials in the face layers to be smaller than those in the core layer. Hence, the size of each resin particle is approximately close to the size of each wooden material in each of the face layers and the core layer. More particularly, the non-uniformity in the mixture due to a difference in the specific gravity between the wooden material (having a specific gravity of 0.4 to 0.6) and the resin particle (having a specific gravity of 0.9) is minimized. Accordingly, the thermoplastic resin particles providing a higher level of the resistance to water will be dispersed uniformly in the whole particle board, thus preventing the resistance to water from being varied locally in the particle board.
This present invention provides the particle board which is improved at its entirety in the residence to water without impairing its performance as a bearing board member.